Mechanical and oxygen-based cues drive a wide array of developmental, homeostatic, and regenerative processes in many if not all tissues; however, the majority of mechanobiology and hypoxic signaling work has been limited to in vitro and in silico environments due to technical limitations of the analytical tools used in vivo. Advances in microelectromechanical systems (MEMS) have created an opportunity to realize a new class of flexible sensors, suitable for incorporation or implantation into biological systems and tissue engineered constructs. Our long term goal is to advance the understanding of oxygen related signaling and mechanobiology by developing a new class of implantable MEMS sensors. We propose to use these sensors to measure the mechanical and oxygen environment locally within different tissue engineered, regenerative environments. The Allen lab has developed numerous microfabrication and microelectromechanical systems (MEMS) strategies, that have enabled the successful design and development of miniaturized sensors from a variety of materials including silicon, metals, ceramics, and polymers. In preliminary studies, we have shown through both in silico analysis and in vitro prototype testing the ability of sensors to fit the complex design criteria of this proposal. Concurrently, the Guldberg lab has established an in vivo, critically sized, segmental bone defect model in the rat which serves as a test-bed to quantitatively screen the efficacy of novel tissue engineered strategies to repair large bone defects. Local measurements of mechanics and oxygen concentration within the regenerating environment in vivo would significantly improve our understanding of tissue regeneration and the fate of tissue engineered constructs. The complimentary expertise of the two labs in MEMS and regenerative medicine, provide the foundation for an interdisciplinary project to locally characterize key factors during tissue regeneration. The objective of this proposal is to develop MEMS sensors that will measure local mechanical stresses and local oxygen tension within a regenerating tissue environment. The following Specific Aims have been designed to fully develop the MEMS technology and to apply it to an in vivo regeneration model: Aim I - To engineer a minimally invasive, implantable MEMS based sensor to measure oxygen concentration and local stress within a tissue engineered construct. Aim II - To characterize temporal changes in oxygen concentration and local mechanics in a critically sized segmental bone defect model. MEMS based devices offer a unique potential to take continuous measurements in vivo in a minimally invasive manner. This research will bring together outstanding expertise from different fields to engineer an innovative new application of MEMS technology which will significantly advance basic understanding of regenerative processes in addition to improving development and pre-clinical evaluation of tissue engineered constructs.